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Rain water tank pumps. How to select the right one!

Updated: Sep 7, 2022

Do you know which is the right pump for your rainwater tank?

If you’ve installed a rainwater tank, or you’re looking at having one in the future, then you’re probably looking to use the stored water in or around your home. To get it to where you need it. You'll need a quality pump. But which pump is best and what should you look out for?

Below we have provided some basic steps to help you understand the type and size of pump you might need for your application, but ultimately we recommend that you seek the assistance of a professional pump retailer.

1) Consider the Application

Knowing how you are going to use your rainwater is an important step in choosing the right pump.

Flow Rate required for the application (in litres per minute) is used as a basis for selecting the right size pump.

  • Outside the home rainwater is regularly used for garden hoses or automatic sprinkler systems to irrigate lawns or whole gardens.

  • Inside the home rainwater is commonly used in laundries and toilets, but if you have a larger rainwater storage tank you might be considering using rainwater for drinking water, showers, handbasins or in the kitchen.

The more taps or outlets you use for rainwater around your home the greater the flow rate required by the pump.

  • Different types of taps or outlets have different flow rates. For example:

  • Household tap/faucet are 15 to 20 litres/minute;

  • A water saver shower head less than 10 litres/minute;

  • Regular shower head/rain head can use 15 to 20 litres/minute;

  • Pop-up sprinkler head 5 to 10 litres/minute.

If you know how many taps or outlets you want to use and then add up the flow rate of each to calculate the total flow rate, then you’ll be able to provide this info to your pump retailer.

Electing a pump for your rainwater tank

2) Pump Type

There are generally two types of pumps used to supply rainwater from a storage tank.


These are installed inside the tank and draw the water through a built-in strainer. These pumps are usually quieter because they are underwater. Maintenance can be more difficult because you will need to remove the pump from the tank and there can be more pipework to worry about, but these are minor considerations. Example of submersible pumps include the Grundfos SB and SBA.

Dry Mount

This type of pump is often installed adjacent to the tank, which makes pipework shorter and maintenance easier. Pump noise is more of a factor with dry mounted pumps but there are very quiet models to choose from in the Grundfos range.

3) Pump features to look out for

Not all domestic rainwater pumps are created equal, so it’s worth familiarising yourself with some of the features of quality pumps.


If your rainwater tank is quite close to the house - or a neighbour’s - then you might want to consider how noisy the pump will be when operating at full capacity. Submersed pumps are already virtually silent, but good examples of very quiet Dry Mounted pumps are the Grundfos CM Booster.

Fixed or Variable Speed

Fixed speed pumps operate at one pace. They are on or off, regardless of how many outlets are open so they are perfect for toilets, laundries, garden irrigation and hand watering. The new Grundfos SCALA1 is a great example of a fixed speed pump.

Whereas variable speed pumps (sometimes called Inverters) adjusts their speed according to demand. This means if you open just one tap the pump speed will be quite low; but open more taps and the pump motor will speed up, achieving the same pressure across all the open outlets.

Because Inverter Pumps vary in their speed, they can save a considerable amount on running costs over the life of the pump. A good example of a very quiet pump is the Grundfos SCALA2 .

Dry-run Protection

This feature stops the pump if the rainwater tank runs dry, preventing serious damage to the pump motor. All pumps in the Grundfos domestic rainwater pump range have dry-run protection built in.

4) Installation

One of the final considerations when purchasing a pump is the installation. Here are some of the basic requirements of a pump installation:


Extension cords are a bad idea so you’ll need to have a power outlet installed near to your pump, and if not under cover it will need to be outdoor rated.


The pump needs to be installed on a firm flat surface, like a concrete pad or large format paver, so the pump doesn’t move around whilst operating.


Pumps are not usually supplied with pipework or the related connections, so you’ll need to ask your pump retailer about requirements for the inlet and outlet pipework of your pump.

Pump Cover

Depending on where your pump is installed - undercover or in the open - you may want to cover your pump using a specifically designed pump cover. This will prevent UV damage by solar rays and reduce pump noise, whilst keeping the pump ventilated during hot weather.

You can trust Grundfos and ABC Pumps & Irrigation

If you’re now ready to take the next step and purchase a pump for your rainwater tank Contact ABC Pumps and Irrigation for the right Grundfos Pump.

Call us on (02) 43881 811.

Locate your nearest Authorised Grundfos Dealer

Your Grundfos Authorised Dealer possesses not only the best LOCAL knowledge, but also a genuine desire to discuss your individual pumping requirements and provide you with a professional solution to meet your needs.

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